The invention is motivated by a keen need for automating and simplifying the time-consuming authoring task used for language-oriented intelligent learning systems. This is because even though the number of possible correct right responses is reasonably limited, it is often necessary to deal with a large, in fact, theoretically unlimited number of plausible errors of learners for developing an ideal learning system. As far as the inventors can judge, at least within the foreseeable future, the state of the art in natural language processing technology cannot reach the level capable of providing a ready solution to an automatic correction of an entirely free format error-ridden sentence. This seems possible only when the world knowledge base of so-called common sense may be introduced into the system so that many competent human teachers can somehow manage to cope with it.